Recently, interests in energy storage technologies have been increasingly grown. In particular, while the application of the energy storage technologies is expanded to mobile phones, camcorders, notebook PCs, and even to electric vehicles, research and efforts for the development of the energy storage technologies have been gradually materialized.
Electrochemical devices have received most attention in the field of energy storage technologies, and there emerges an interest in rechargeable secondary batteries among these electrochemical devices.
Among the currently used secondary batteries, lithium secondary batteries, developed in the early 1990's, are spotlighted because the lithium secondary batteries may have higher operating voltage and significantly higher energy density.
The lithium secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte solution including an electrolyte solution solvent and an electrolyte salt.
Since the electrolyte solution solvent is decomposed on a surface of an electrode during charge and discharge of the battery or collapses a negative electrode structure by being co-intercalated between the carbon negative electrode layers, the electrolyte solution solvent may degrade stability of the battery.
It is known that this limitation may be addressed by a solid electrolyte interface (SEI) film which is formed on the surface of the negative electrode by the reduction of the electrolyte solution solvent during initial charge of the battery.
However, the SEI film may be easily collapsed over time by electrochemical energy and thermal energy when the lithium secondary battery is operated or left standing in a high-temperature environment. In a case in which the SEI film is collapsed, the negative electrode is exposed, and gases, such as CO, CO2, CH4, and C2H6, are generated while the exposed negative electrode reacts with the electrolyte solution to continuously cause a side reaction.
As a result, since a battery internal pressure increases to cause an internal short circuit of the battery as well as battery deformation such as battery swelling, fire or explosion of the battery may occur.
Recently, a method of adding an additive for forming an SEI film to prevent the collapse of the SEI film in the non-aqueous electrolyte solution has been proposed. However, eventually another limitation has occurred in which irreversible capacity of the secondary battery is increased and output characteristic are reduced while an electrolyte solution oxidation reaction occurs on the surface of a positive electrode during a high-temperature reaction due to the electrolyte solution additive.
In order to address these limitations, there is a need to develop a non-aqueous electrolyte solution and a lithium secondary battery which may reduce gas generation during high-temperature storage.